1. Field of the Invention
The present invention relates to a method for controlling an aircraft light so as to emit a desired light intensity taking into consideration the aging behavior of the LED light sources of the aircraft light and compensating for the aging effect of the LEDs.
2. Description of the Prior Art
In the field of interior and exterior aircraft lights, during the last decades more and more LEDs are used as light sources. As in case of electronic components in general as well as in case of other electro-optical components, LEDs are subjected to aging. This results in a reduced intensity of the light emitted by the LEDs throughout their lifetime which can be compensated by increasing the power supply to the LEDs.
It is known in the art to sense the aging degradation of LEDs by means of sensors detecting the light intensity emitted by an LED. Examples of these designs can be found in EP-B-1 825 188, DE-A-102 48 238, DE-B-102 57 184, DE-A-197 54 222, DE-A-10 2008 020 382, DE-A-10 2009 006 250, WO-A-99/56303, WO-A-2008/104228, and U.S. Pat. No. 6,236,331.
It is also known in the prior art to compensate for any aging degradation of LEDs. Examples of lights using this compensation concept can be found in DE-A-199 17 239, DE-C-102 01 908, DE-A-10 2004 060 201, DE-A-10 2005 018 175, DE-A-10 2006 054 512, DE-A-10 2008 064 397, DE-A-10 2009 031 403, WO-A-96/09667, WO-A-01/71444, and U.S. Pat. No. 4,182,977.
When compensating for aging degradations of LEDs, one has to sense the light intensity of an LED throughout its lifetime. The aging degradation is dominated in the first place by the temperature of the LED, i.e. the environmental temperature and/or the operational temperature of the LED. For sensing the light intensity, an optical sensor is necessary. However, depending on the aircraft light design, it can be difficult to place an optical sensor within the housing of the aircraft light due to limited space and/or due to the fact that the optical sensor might cause shielding effects and a reduced light yield because the light of an LED impinging on the optical sensor can no longer be used for the illumination desired.
Therefore, it is already suggested in the prior art to observe a reference LED instead of an LED used to emit the desired light. DE-U-20 2007 005 003 discloses such a light which can be used as an aircraft safety light as used on e.g. tall building structures. In this known light, a photo sensor is associated to the reference LED which emits its light to the photo sensor only and which is shielded or shut off otherwise. However, such an operation of a reference LED cannot represent the operational and environmental conditions which the primary or main LEDs of the light are subjected to throughout their lifetime.
WO-A-2010/139059 discloses a light emitting device comprising a light emitting reference unit which is monitored so as to detect variations in the output of the reference unit arising from changes in temperature or other environmental conditions. The light emitting device is controlled so as to compensate for the output variation of the reference unit detected.
Moreover, from US-A-2008/0238343 a system and method for dimming at least one light source is known while in WO-A-2010/036789 methods and systems for maintaining the illumination intensity of LEDs are described.
Accordingly, there is a need in the prior art for improving the simulation of the operational and environmental conditions of the LEDs of an aircraft light.